1. Field of the Invention
The present invention relates to an engine starter for starting an engine.
2. Description of the Related Art
Conventionally, engine starters which are driven by a battery are known. Japanese Unexamined Patent Application, First Publication, No. Hei 9-310677 discloses an example of a starter, in which an epicyclic (or planetary) ring gear is flexibly supported by a case, so that the engagement between gear wheels is loosened and the rattling state due to backlash is reduced, thereby reducing noise.
Japanese Unexamined Patent Application, First Publication, No. Hei 9-280145 discloses another example, in which the rotation of the starter motor at the initial phase of the engagement between the ring gear and the pinion gear is restricted, thereby reducing the impact at the initial phase of the engagement. Simultaneously, an epicyclic ring-type reduction gear is loosely attached to a case so as to absorb the impact when the ring gear and the pinion gear are engaged.
Japanese Unexamined Patent Application, First Publication, No. Hei 7-119600 discloses another example of the starter, in which an epicyclic ring-type reduction gear is made of a resin, and is attached to the case in a rotatable form, so that the impact due to unsatisfactory engagement caused by backlash is reduced.
Japanese Unexamined Patent Application, First Publication, No. Hei 8-319923 also discloses another example, in which the slip torque of a one-way clutch is smaller, and the backlash of the ring and pinion gears much more easily disappears, the free running time of the motor is smaller, and the relative rotational difference between the starter motor and the ring gear is canceled, so that the impact and noise generated when the gear faces hit each other are reduced.
In the above conventional engine starters, an impact or vibration transmission, caused by a rattling state of the reduction gear which is positioned between the starter motor and the driven shaft of the engine, can be reduced in some degree. However, it is very difficult to completely remove such a rattling state in the reduction gear. In order to reduce the rattling state, it is effective to improve the accuracy of each gear wheel, or to provide a xe2x80x9cno-backlashxe2x80x9d mechanism (which causes no backlash). However, these means increase the necessary cost, and are generally not suitable for mass production. In addition, pinion-gear engaged starters, which are currently the most common type, require some backlash, so that the workable no-backlash mechanisms or means for reducing the backlash are limited.
Recently, in order to reduce fuel consumption, an idle stop system for stopping the engine in the idling operation has gradually become practical. In a vehicle having such an idle stop system, the starting operation is much more frequently executed; thus, with the above-explained engine starter, impacts or noises are generated and the product value may be degraded. This problem should be solved if the idle stop system is to be employed in a vehicle.
In order not to generate the noises at the start of the vehicle, the engine crankshaft or the like may be directly driven without using a reduction gear (an example thereof is disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 8-193531). However, in this case, a motor outputting high power, a high-voltage power supply, and the like are necessary, so that the weight of the vehicle body is increased, flexibility of the arrangement of each device is degraded, and the cost is considerably increased.
In consideration of the above circumstances, an objective of the present invention is to provide an engine starter for preventing undesirable noise, which is applicable to a vehicle employing an idle stop system.
Therefore, the present invention provides an engine starter for starting an engine, comprising:
a starter motor;
a traction-drive type reduction gear connected to the starter motor and positioned between the starter motor and a driven shaft of the engine; and
a torque transmitting device via which the reduction gear and the driven shaft are linked.
The reduction gear may be coupled with a crankshaft or a cam shaft of the engine.
According to the above structure, the characteristics of the traction-drive type reduction gear are effectively used for performing smooth reduction, and the crankshaft of the engine can be smoothly driven via the torque transmitting device. Therefore, the quietness at the engine start can be improved; thus, the starter can also be applied to a vehicle which employs an idle stop system.
The torque transmitting device may comprise a belt and a pulley for transmitting the torque. Accordingly, the reduction gear ratio of the above structure can be large by using the reduction gear and the belt, thereby reducing the size of the starter.
The belt of the torque transmitting device may also function as a belt for driving auxiliaries of the engine. Accordingly, a belt for driving such auxiliaries can also be used as the belt for transmitting the torque, and thus no additional belt for the torque transmitting device is necessary. Therefore, the number of necessary parts can be reduced. In addition, a longer crankshaft in the engine is unnecessary. Therefore, preferable flexibility of the arrangement of the starter can be obtained.
The engine starter may be positioned via a pulley at a most tightly curved portion of the belt for driving the auxiliaries of the engine. This arrangement does not affect the position of a tensioner used for the belt for driving the auxiliaries. Therefore, modification of the general structure in the vicinity of the engine is unnecessary, and the starter can be easily mounted.
The traction-drive type reduction gear may be a wedge-roller type. In this case, the reduction gear has the function of a one-way clutch. Therefore, a conventional one-way clutch can be omitted, and the axial length of the starter motor can be reduced. Accordingly, the weight and the number of parts of the starter can be decreased, thereby remarkably reducing the cost.
Typically, the driven shaft of the engine is one of a crankshaft and a cam shaft. Accordingly, the engine can be started not by using gears but by using a starter motor that rotates the crankshaft or cam shaft. Therefore, the engine can be quietly started.